Am3O9(M2O4)n : A series of oxides derived from the rutile structure by chemical twinning

Abstract

A series of oxides AM3O9(M2O4)n derived from the rutile structure by chemical twinning have been isolated and characterized by X-ray and electron diffraction. Pure phases are isolated for the members n = 2− K1−xNaxTi2Nb5O17 (O ⩽ × ⩽ 0.50),K1−xBaxTi2+xNb5−xO17 (O ⩽ × ⩽ 1),KTi2−2xFexNb5+xO17 (O ⩽ × ⩽ 0.40),KTi2−3xCuxNb5+2xO17 (O ⩽ × ⩽ 0.20) and KTi2−xNb5+xO17 (O ⩽ × ⩽ 1.75) − n = 4 − NaTi6Nb5O25 and BaTi7Nb4O25 and n = 5− KTi8Nb5O29. The member n = 3 (KTi4Nb5O21) and the intergrowth n = 4.5 (KTi7Nb5O27) were observed in the form of pure microcrystal by electron diffraction, but X-ray diffraction patterns show that they are always accompanied by a mixture of the more stable phases n = 2 and or 4 and TiO2. The structural evolution and the stability of these oxides is discussed.